1. Field of the Invention
The invention described herein is generally related to vehicle transmission systems, and in particular, to clutchless transmissions.
2. Description of the Related Art
FIG. 1 shows a diagrammatic representation of a typical vehicle 100 and drive-train 101. An internal combustion engine 102 provides rotational energy to an engine output shaft 104, which is coupled to the wheels 106 to provide motive power to the vehicle 100. The engine 102 operates in a range of around 1,000 to 6,000 rpms, and delivers the highest power and efficiency within a much smaller range.
Because the optimum operating range of the engine 102 is limited, a transmission 108 is employed to change a coupling ratio between the output shaft 104 and the wheels 106. Gears internal to the transmission 108 are coupled in various configurations to achieve several different coupling ratios so that the vehicle 100 can operate over a wide range of speeds while the engine 102 remains substantially within its optimum range of rpms.
The engine 102 comprises many moving parts, including pistons, valves, camshaft, flywheel, etc. During operation, the engine 102 develops a high degree of output inertia due to the mass of the moving parts. At the same time, the vehicle develops inertia of its own as it travels at speed. If the engine 102 were directly coupled to the transmission 108, a change of coupling ratios would require an instantaneous change in the rotational speed of the engine 102 or the speed of the vehicle 100, or a combination of both. The sudden torque load of such an instantaneous transition would be devastating to the entire drive-train 101, and extremely uncomfortable to vehicle occupants. Additionally, if the engine were directly coupled to the transmission, it would be impossible to stop the vehicle 100 without shutting down the engine 102.
In order to permit gear changes that are tolerable to the vehicle and occupants, a clutch 110 is employed to provide torque compensation between the engine 102 and the transmission 108. The clutch interrupts the torque from the engine 102 while the gears are changed, then engages the engine 102 to the transmission 108 gradually so that the speed of the engine 102 can adapt to the speed of the vehicle 100, as translated through the new gear ratio.
Various types of clutches are known, including dry clutches and fluid clutches. A torque converter is a type of fluid clutch typically employed in automatic-transmission vehicles, while standard transmission vehicles generally use a diaphragm clutch 110, as illustrated in FIG. 2.
The clutch 110 of FIG. 2 includes a flywheel 122 coupled to an output shaft 104 of an engine. The output shaft may be, for example, the crank shaft of an internal combustion engine. The clutch 110 further includes a clutch plate 130, a pressure plate 128, a diaphragm spring 126, a cover 124, studs 136, and a throw-out bearing 134. The clutch plate 130 is coupled to a transmission input shaft 132.
The flywheel 122, clutch cover 124, diaphragm spring 126, and pressure plate 128 all rotate with the engine output shaft 104. The clutch plate 130 is rigidly coupled to the input shaft 132 of the transmission 108. When the throw-out bearing 134 presses against the diaphragm spring 126, it pivots on studs 136 linking the spring 126 to the cover 124, and lifts the pressure plate 128 from the clutch plate 130, disengaging the engine 102 from the transmission 108 (as shown in FIG. 2). When fully disengaged, the transmission 108 can change gears or the vehicle 100 can come to a stop without affecting the rotation of the engine 102.
As the bearing 134 withdraws, the spring 126 presses the pressure plate 128 against the clutch plate 130 with progressively greater force. Torque from the engine 102 is gradually transferred to the transmission 108 as friction increases between the plates 128, 130, until the transmission 108 and the engine 102 are again fully and rigidly coupled.
The clutch plate 130 has some output inertia of its own, which is typically compensated for during gear changes by synchronizers in the transmission 108.